1. Field of the Invention
The present invention relates to the production of organic acids and salts thereof from polysaccharides, and more particularly to a method of producing high yields of glycolic and oxalic acids by treatment of polysaccharide-containing materials with a concentrated alkaline solution.
2. Description of the Art
Glycolic acid (HOCH.sub.2 COOH) has several important commercial uses including textile and leather processing; metal cleaning and plating; dairy and food processing sanitation; water well cleaning; masonry cleaning; and production of detergents, adhesives, coatings, and biodegradable polymers. Presently, glycolic acid is produced commercially as an intermediate in one of the processes used for the manufacture of ethylene glycol. This process involves the production of methanol and formaldehyde as intermediates before glycolic acid. The conversion of formaldehyde to glycolic acid requires reaction with carbon monoxide, water, and an acid catalyst at very high pressures, and thus, is very costly. An alternative to the present multi-step method, and in particular, a method wherein high yields of glycolic acid could be readily obtained from polysaccharide material, for example, excess or waste agricultural materials such as starch, corn cobs, cotton waste, and straw residue, would be of great use.
Oxalic acid [(COOH).sub.2 ] is used commercially for many purposes, for example, as an analytical reagent, in textile and leather processing, in metal cleaning, and as an intermediate for many chemical compounds. Presently, oxalic acid is obtained commercially by passing carbon monoxide into concentrated sodium hydroxide or by heating sodium formate in the presence of sodium hydroxide or sodium carbonate. As with glycolic acid, a method to obtain high yields of oxalic acid from inexpensive polysaccharide sources would be of great value.
Production of organic acids from the reaction of alkali with cellulosic materials is known. Bannister (U.S. Pat. No. 1,972,059) reported the production of primarily acetic, oxalic, formic, and succinic acids, but no glycolic or lactic acids, by alkaline fusion of cellulosic materials in a closed vessel under pressure. A critical feature of the Bannister method is that the cellulosic material, e.g., corn cobs, is fused with caustic soda and small amounts of water (water-to-alkali ratios of 0.2 to 0.6) under pressures of 50 or 75 pounds per square inch (psi). Bannister found that 50 or 75 psi gave results as good as much higher pressures. The reason for the low pressures was the small amount of water Bannister used relative to caustic and cellulosic material.
Chesley et al. (U.S. Pat. No. 2,750,414) reported the production of saturated monocarboxylic acids having 1-3 carbon atoms, principally formic, lactic, acetic, and glycolic acids, by the reaction of celluosic materials in dilute aqueous alkaline solutions at elevated temperatures in a closed system. While a water-to-alkali ratio of 3.5 was used by Chesley et al. (Table 2, run 2), most of the reactions were carried out at water-to-alkali ratios of about 15 and above. In the Chesley et al. process, the formation of oxalic acid does not occur to any substantial extent. A feature of the Chesley et al. method that distinguished it from Bannister is that the celluosic materials had to be reacted with alkali and water in the liquid phase. Thus, although the alkali-to-cellulosic material ratio was approximately the same as Bannister, the water-to-alkali ratio was approximately one to two orders of magnitude larger, and the water-to-cellulosic ratio was much larger. The reaction mixture was a very liquid, free-flowing slurry of cellulosic material in dilute aqueous alkaline solution, compared to Bannister's non-liquid, non-free-flowing, dry-like reaction mass. Given the temperatures studied by Chesley et al. and the larger amount of water used in their closed vessel system, the autogenously developed pressures (about 560-1250 psi) are much greater than Bannister.